It is often desirable to know the location of a terminal such as a cellular phone. For example, a location services (LCS) client may desire to know the location of a terminal in the case of an emergency services call or to provide some service to the user of the terminal such as navigation assistance or direction finding. The terms “location” and “position” are synonymous and are used interchangeably herein.
One method of determining the location of Mobile Stations (MS′) is based on measurements of the times of signal arrival from multiple antennas. For example, an MS may measure time differences in received signals from a plurality of base station antennas. Because positions of the base station antennas are known, the observed time differences may be used to calculate the location of the terminal.
An MS may make use of a Base Station Almanac (BSA) to perform measurement calculations and/or may send the measurements to a location server for position calculation. The term Advanced Forward Link Trilateration (AFLT) is used to describe terrestrial positioning in Code Division Multiple Access (CDMA) systems, while the term Observed Time Difference of Arrival (OTDOA) is used in the context of Wideband CDMA (WCDMA) and Long Term Evolution (LTE) systems.
Typically, accuracy in terrestrial positioning is dependent on synchronization of base station clocks and signal transmissions. However, variations in hardware and installation procedures may cause variations in inter-cell synchronization on the order of hundreds of nanoseconds. Even a 100 nanosecond synchronization variation between cells translates into 30 meters of ranging error. Therefore, for optimal performance, terrestrial positioning systems require calibration.
However, current calibration procedures are cumbersome and resource intensive, and often involve significant field data collection in the vicinity of every cell transmitter in a network. Additionally, calibrations change with time due to network maintenance and/or reconfiguration. Thus, in existing systems, resource intensive calibration work is repeatedly performed for optimum positioning performance. Consequently, deployment interest in terrestrial positioning systems has waned because of resource intensive nature of terrestrial positioning system calibration.
Therefore, there is a need for systems and methods to facilitate terrestrial positioning system calibration, thereby improving terrestrial positioning system deployment and utilization.